Late post-injection fueling strategy in a multi-cylinder diesel engine during regeneration of an exhaust after-treatment device

ABSTRACT

A strategy for late post-injection fueling in a diesel engine ( 10 ) that can mitigate scuffing and wear due to cylinder wall washing by late post-injected fuel that is needed for regenerating an exhaust after-treatment device ( 38 ).

FIELD OF THE INVENTION

This invention relates generally to internal combustion engines,especially compression ignition (i.e. diesel) engines. Morespecifically, the invention relates to a strategy for latepost-injection of fuel while an exhaust after-treatment device is beingregenerated.

BACKGROUND OF THE INVENTION

Examples of after-treatment devices for treating exhaust gas passingthrough an exhaust system of a diesel engine are a diesel particulatefilter (DPF) and a NOx adsorber catalyst. After-treatment devicespromote chemical reactions and/or trap particulate matter in exhaustflowing through the exhaust system from the engine, thereby preventingsignificant amounts of pollutants such as hydrocarbons, carbon monoxide,soot, SOF, and ash, from entering the atmosphere.

These after-treatment devices typically require regeneration from timeto time in order to keep them effective and prevent them for becomingineffective and/or even detrimental to engine performance due to thematter that they collect. For example, trapped soot in a DPF must beburned off before it restricts exhaust flow to such an extent that itcauses engine back-pressure to increase to undesired levels.

One way to create conditions for initiating and sustaining regenerationof a DPF involves elevating the temperature of exhaust gas entering theDPF to a sufficiently high temperature to burn off trapped soot. Becausea diesel engine typically runs relatively cool and lean, the latepost-injection of diesel fuel can be used as part of a strategy toelevate temperature of exhaust gas entering the DPF while still leavingexcess oxygen for burning the trapped particulate matter. Latepost-injection of fuel into an engine cylinder during an expansionstroke conditions the exhaust with additional unburned fuel. Anoxidation catalyst ahead of the DPF promotes combustion of thepost-injected fuel, sufficiently elevating the temperature of exhaustentering the DPF to initiate and sustain regeneration of the DPF.

The nature of conventional diesel combustion comprises a main injectionof fuel into an engine cylinder when the piston that reciprocates in thecylinder arrives essentially at top dead center (TDC) at the end of acompression stroke. The fuel injector may inject diesel fuel as one ormore directed streams that are aimed toward a bowl in the piston headwhen the piston is essentially at TDC. The injected fuel combusts toforce the piston away from the fuel injector. Late in the expansiondownstroke, the piston is moving away from the fuel injector over arange of positions that are out of the way of the paths that injectedfuel stream from the fuel injector would follow and the gas density inthe cylinder has been significantly reduced.

SUMMARY OF THE INVENTION

The inventors have observed that as a consequence of this combustionchamber geometry, the late post-injection of diesel fuel needed tocreate conditions for regeneration of an exhaust treatment device maycause one or more injected fuel streams to miss the down-stroking pistonand instead hit the cylinder wall. This can result in the diesel fuelwashing the film of engine motor oil on the cylinder wall.

During the ensuing exhaust upstroke, rings of the upstroking piston willwipe across zones of the cylinder wall that may have been washed. Thereduced lubricity in those zones due to the prior washing may promotescuffing and wear that would not occur in the absence of such latepost-injections.

In the absence of the present invention, it seems a virtual certaintythat every engine cycle of every cylinder would have its cylinder wallwashed to some extent by late post-injected diesel fuel.

Briefly, the present invention relates to a strategy for latepost-injection fueling that can mitigate scuffing and wear due tocylinder wall washing by late post-injected fuel that is needed forregenerating an exhaust after-treatment device.

The strategy is embodied in the engine control system as a programmedalgorithm that is repeatedly executed by a processor.

One generic aspect of the present invention relates to a method of latepost-injection of diesel fuel into cylinders of a multi-cylinder dieselengine for creating exhaust, which during passage through an exhaustsystem that includes an after-treatment device, is effective toregenerate the after-treatment device. During a series of maincombustion events that occur in succession in a group of cylinders in arepetitive engine cycle for the cylinders, a late post-injection controlstrategy causes a late post-injection of diesel fuel into at least onebut fewer than all cylinders of the group.

Another generic aspect of the invention relates to a diesel enginecomprising engine cylinders within which diesel fuel is combusted, anexhaust system, including an after-treatment device, through whichexhaust resulting from in-cylinder combustion passes, and a controlsystem for controlling injection of diesel fuel into the cylinders,including main injections and late post-injections of diesel fuel. Thecontrol system contains a strategy for late post-injections of dieselfuel to create exhaust suitable for regenerating the after-treatmentdevice, and when executing the strategy, causes a late post-injection ofdiesel fuel into at least one but fewer than all cylinders of a group ofcylinders during a series of main injections that occur in succession inthe group of cylinders in a repetitive engine cycle.

The foregoing, along with further features and advantages of theinvention, will be seen in the following disclosure of a presentlypreferred embodiment of the invention depicting the best modecontemplated at this time for carrying out the invention. Thisspecification includes drawings, now briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic diagram of those portions of an exemplarydiesel engine relevant to principles of the present invention.

FIG. 2 is a table presenting several different embodiments of theinventive strategy.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows schematically a portion of an exemplary turbocharged dieselengine 10 for powering a motor vehicle. Engine 10 comprises sixcylinders 12 within which pistons reciprocate. Each piston is coupled toa respective throw of a crankshaft by a corresponding connecting rod.Engine 10 further comprises an intake system 14 and an exhaust system16. Turbocharging is provided by a turbocharger 18 having a turbine 20in exhaust system 16 that operates a compressor 22 in intake system 14.

Intake system 14 further comprises an intercooler 24 downstream ofcompressor 22 for cooling charge air that has been drawn into intakesystem 14 and compressed by compressor 22. From intercooler 24 thecharge air is introduced into an engine intake manifold 26 that servescylinders 12. Charge air enters each cylinder when a respective intakevalve is open during the engine cycle.

Engine 10 further comprises a fueling system 28 that comprises fuelinjectors 30 for cylinders 12. The engine also has a processor-basedengine control system or unit (ECU) 32 that processes data from varioussources to develop various control data for controlling various aspectsof engine operation. The data processed by ECU 32 may originate atexternal sources, such as various sensors 34, and/or be generatedinternally. Examples of data processed may include engine speed, intakemanifold pressure, exhaust manifold pressure, fuel injection pressure,fueling quantity and timing, mass airflow, and accelerator pedalposition.

Engine 10 further comprises a low-pressure EGR system 36 that comprisesan EGR cooler 40 and EGR valve 42 between exhaust system 16 and intakesystem 14.

A diesel particulate filter (DPF) 38 is an exhaust after-treatmentdevice disposed in the exhaust system downstream of turbine 20.

ECU 32 controls engine fueling by controlling the operation of thefueling system 28, including controlling the operation of the fuelinjectors 30. The processing system embodied in ECU 32 can process datasufficiently fast to calculate, in real time, the timing and duration ofdevice actuation to set both the timing and the amount of each injectionof fuel into a cylinder.

ECU 32 also controls regeneration of DPF 38. When ECU 32 determines aneed to regenerate DPF 38 as a result of processing certain datarelevant to the determination, it alters the fueling strategy to causelate post-injection of diesel fuel.

In accordance with principles of the present invention, during a seriesof main combustion events that occur in succession in a group ofcylinders in a repetitive engine cycle for the cylinders, ECU 32executes a late post-injection control strategy that causes a latepost-injection of diesel fuel into at least one but fewer than allcylinders of the group.

The table of FIG. 2 presents different implementations of the strategy.The top horizontal row of the table contains a time sequence, with timerunning horizontally from left to right, of six successive repetitionsof the cylinder engine cycle (153624) for engine 10. This sequencerepeats during regeneration.

A first example of late post-injection fueling strategy is designated“Post-Injection A”. During the first occurrence of the engine cycle, alate post-injection of diesel fuel is made only into Cylinder No. 1.During the second occurrence of the engine cycle, a late post-injectionof diesel fuel is made only into Cylinder No. 5. During the thirdoccurrence of the engine cycle, a late post-injection of diesel fuel ismade only into Cylinder No. 3. During the fourth occurrence of theengine cycle, a late post-injection of diesel fuel is made only intoCylinder No. 6. During the fifth occurrence of the engine cycle, a latepost-injection of diesel fuel is made only into Cylinder No. 2. Duringthe sixth occurrence of the engine cycle, a late post-injection ofdiesel fuel is made only into Cylinder No. 4.

According to example “Post-Injection A”, during a sequence of successiverepetitive occurrences of the cylinder engine cycle equal in number tothe number of cylinders in a group of cylinders (six cylinders for thisparticular example), a late post-injection of diesel fuel is made intoonly a single one of cylinders 12 during each repetition of the enginecycle, and during the sequence no cylinder receives more than one latepost-injection of diesel fuel.

It is also to be noticed that during the sequence of “Post-Injection A”,successive late post-fuel injections of diesel fuel are made inrespective cylinders in the same order as in the engine cycle, namely alate post-injection in cylinder No. 1 during the first occurrence of theengine cycle, a late post-injection in cylinder No. 5 during the secondoccurrence of the engine cycle, . . . etc.

The example “Post-Injection B” contains two successive identicalsequences, each having three successive repetitions of the engine cycle.The number of repetitions in each sequence is equal to one-half thenumber of six cylinders in the group. According to “Post-Injection B”,during each of the two identical sequences, a late post-injection ofdiesel fuel is made into each of two cylinders 12 during each of threesuccessive repetitions of the engine cycle, and each of the sixcylinders receives only one late post-injection of diesel fuel over thecourse of the three successive repetitions of the engine cycle in eachof the two sequences. It should also be noticed that during eachrepetition of the engine cycle, the two late post-injections of dieselfuel occur in successive cylinders in the engine cycle.

The example “Post-Injection C” shows three consecutive identicalsequences from left to right. Each sequence comprises two repetitions ofthe engine cycle, making the number of repetitions in each sequenceequal to one-third the number of six cylinders in the group. Thisexample is somewhat similar to example “Post-Injection B” in that duringeach repetition of the engine cycle, a late post-fuel injection ofdiesel fuel is made into each of three successive cylinders in theengine cycle while no late post-injection of diesel fuel is made intothe other three cylinders. The two consecutive repetitions of the enginecycle in each of the three sequences cause every cylinder to receiveexactly one late post-injection of diesel fuel during the respectivesequence.

The example “Post-Injection D” shows that during each repetition of theengine cycle, each of four different cylinders receives a late post-fuelinjection of diesel fuel, but not the other two. The post-injectionsduring each repetition of the engine cycle are not always consecutive,as shown by the third and sixth repetitions.

The example “Post-Injection E” shows that during each repetition of theengine cycle, each of five different cylinders receives a late post-fuelinjection of diesel fuel, but not the other one. The post-injectionsduring each repetition of the engine cycle are not always consecutive,as shown by the third through sixth repetitions.

During the progress of an on-going regeneration, a control strategy maychange late post-injection from one example to another, and may even usea strategy that is not specifically shown by the examples of FIG. 2. Thequantity and the specific timing of late post-injected fuel may alsochange depending on factors related to engine operation and the state ofregeneration progress. Also a post-injection may comprise either asingle fuel pulse or multiple fuel pulses. It is to be appreciated thatprinciples of the invention disclosed in the examples presented hereapply to any multi-cylinder engine.

While a presently preferred embodiment of the invention has beenillustrated and described, it should be appreciated that principles ofthe invention apply to all embodiments falling within the scope of thefollowing claims.

1. A method of late post-injection of diesel fuel into cylinders of amulti-cylinder diesel engine for creating exhaust, which during passagethrough an exhaust system that includes an after-treatment device, iseffective to regenerate the after-treatment device, the methodcomprising: during a series of main combustion events that occur insuccession in a group of cylinders in a repetitive engine cycle for thecylinders, executing a late post-injection control strategy that causesa late post-injection of diesel fuel into at least one but fewer thanall cylinders of the group.
 2. A method as set forth in claim 1 whereinduring a sequence of successive repetitions of the engine cycle equal innumber to the number of cylinders in the group, a late post-injection ofdiesel fuel is made into only a single cylinder during each repetitionof the engine cycle, and during the sequence no cylinder receives morethan one late post-injection of diesel fuel.
 3. A method as set forth inclaim 2 wherein during the sequence, successive late post-fuelinjections of diesel fuel are made into cylinders in the same order asthe engine cycle.
 4. A method as set forth in claim 1 wherein during asequence of successive repetitions of the engine cycle equal in numberto one-half the number of cylinders in the group, a late post-fuelinjection of diesel fuel is made into each of multiple cylinders duringeach repetition of the engine cycle, and during the sequence no cylinderreceives more than one late post-injection of diesel fuel.
 5. A methodas set forth in claim 1 wherein during a sequence of successiverepetitions of the engine cycle equal in number to one-third the numberof cylinders in the group, a late post-fuel injection of diesel fuel ismade into each of multiple cylinders during each repetition of theengine cycle, and during the sequence no cylinder receives more than onelate post-injection of diesel fuel.
 6. A method as set forth in claim 1wherein during a sequence of successive repetitions of the engine cycleequal in number to the number of cylinders in the group, a latepost-injection of diesel fuel is made into each of more than one-halfthe number of cylinders in the group during each repetition.
 7. A methodas set forth in claim 6 wherein during each repetition of the enginecycle, the late post-injections of diesel fuel are made into respectivecylinders in succession in the same order as the engine cycle.
 8. Adiesel engine comprising: engine cylinders within which diesel fuel iscombusted; an exhaust system, including an after-treatment device,through which exhaust resulting from in-cylinder combustion passes; acontrol system for controlling injection of diesel fuel into thecylinders, including main injections and late post-injections of dieselfuel, wherein the control system contains a strategy for latepost-injections of diesel fuel to create exhaust suitable forregenerating the after-treatment device, and when executing thestrategy, causes a late post-injection of diesel fuel into at least onebut fewer than all cylinders of a group of cylinders during a series ofmain injections that occur in succession in the group of cylinders in arepetitive engine cycle.
 9. A diesel engine as set forth in claim 8wherein during a sequence of successive repetitions of the engine cycleequal in number to the number of cylinders in the group, execution ofthe strategy causes a late post-injection of diesel fuel to be made intoonly a single cylinder during each repetition of the engine cycle and nocylinder to receive more than one late post-injection of diesel fuelduring the sequence.
 10. A diesel engine as set forth in claim 9 whereinexecution of the strategy during the sequence causes successive latepost-fuel injections of diesel fuel to be made into respective cylindersin the same order as the engine cycle.
 11. A diesel engine as set forthin claim 8 wherein during a sequence of successive repetitions of theengine cycle equal in number to one-half the number of cylinders in thegroup, execution of the strategy causes a late post-fuel injection ofdiesel fuel to be made into each of multiple cylinders during eachrepetition of the engine cycle and no cylinder to receive more than onelate post-injection of diesel fuel.
 12. A diesel engine as set forth inclaim 8 wherein during a sequence of successive repetitions of theengine cycle equal in number to one-third the number of cylinders in thegroup, execution of the strategy causes a late post-fuel injection ofdiesel fuel to be made into each of multiple cylinders during eachrepetition of the engine cycle and during the sequence no cylinder toreceive more than one late post-injection of diesel fuel.
 13. A dieselengine as set forth in claim 8 wherein during a sequence of successiverepetitions of the engine cycle equal in number to the number ofcylinders in the group, execution of the strategy causes a latepost-injection of diesel fuel to be made into each of more than one-halfthe number of cylinders in the group during each repetition.
 14. Adiesel engine as set forth in claim 13 wherein during each repetition ofthe engine cycle, execution of the strategy causes the latepost-injections of diesel fuel to be made into respective cylinders insuccession in the same order as the engine cycle.